Mohr obfuscates issues in his discussion of partial collapses of buildings, such as Windsor Tower and Delft University. He claims that these steel-reinforced concrete buildings should have resisted fire even better than the three WTC skyscrapers, which were steel-framed buildings.

Steel is a good conductor and concrete is a poor conductor of heat. Thus in a fire, a steel frame will conduct heat away from the hotspots into the larger structure. As long as the fire does not consume the larger structure, this heat conductivity will keep the temperatures of the frame well below the fire temperatures. The same is not true of steel-reinforced-concrete structures, since concrete is not a good thermal conductor, and the thermal conductivity of the rebar inside the concrete is limited by its small mass and the embedding matrix of concrete.

Fires can cause spalling of concrete, but not of steel. This is because concrete has a small percentage of latent moisture, which is converted to steam by heat. Thus, a large fire can gradually erode a concrete structure to the point of collapse, whereas a fire can only threaten a steel-framed structure if it elevates steel temperatures to such an extent that it causes failures.

Hoffman's discussion of the Windsor Building fire is recommended reading and also relevant to the partial collapse of the Delft University.

Mohr argues that the precise 42-inch sagging figure (as against the 3 inches that the NIST fire tests produced) could somehow have been deduced from the claimed inward pulling of the buildings' exterior columns, based only on scant photographic evidence. As regards its fire experiment, NIST writes:

NIST contracted with Underwriters Laboratories, Inc. to conduct tests to obtain information on the fire endurance of trusses like those in the WTC towers[...] All four test specimens sustained the maximum design load for approximately 2 hours without collapsing[...] The Investigation Team was cautious about using these results directly in the formulation of collapse hypotheses. In addition to the scaling issues raised by the test results, the fires in the towers on September 11, and the resulting exposure of the floor systems, were substantially different from the conditions in the test furnaces. Nonetheless, the [empirical test] results established that this type of assembly was capable of sustaining a large gravity load, without collapsing, for a substantial period of time relative to the duration of the fires in any given location on September 11.

Summing up: some low, poorly planned and constructed steel buildings have indeed totally collapsed from fires; an oil rig mostly collapsed from an explosion and fires fed by an unlimited fuel and oxygen; and parts of buildings with a steel-reinforced concrete structure (much more prone to fire damage) have collapsed. However, a sudden total collapse of a skyscraper like WTC 7, in which 80 steel columns (or, in the case of its facade, 58 columns) had to snap without providing even a minimum of resistance throughout 8 floors – NIST acknowledged in the fnal report that the skyscraper underwent "a freefall descent over approximately eight stories at gravitational acceleration for approximately 2.25 seconds" – represents a completely different kind of case.